Exploring the “Goldilocks Zone” of Semiconducting Polymer Photocatalysts by Donor–Acceptor Interactions

Abstract

Water splitting using polymer photocatalysts is a key technology to a truly sustainable hydrogen‐based energy economy. Synthetic chemists have intuitively tried to enhance photocatalytic activity by tuning the length of π‐conjugated domains of their semiconducting polymers, but the increasing flexibility and hydrophobicity of ever‐larger organic building blocks leads to adverse effects such as structural collapse and inaccessible catalytic sites. To reach the ideal optical band gap of about 2.3 eV, A library of eight sulfur and nitrogen containing porous polymers (SNPs) with similar geometries but with optical band gaps ranging from 2.07 to 2.60 eV was synthesized using Stille coupling. These polymers combine π‐conjugated electron‐withdrawing triazine (C3N3) and electron donating, sulfur‐containing moieties as covalently bonded donor–acceptor frameworks with permanent porosity. The remarkable optical properties of SNPs enable fluorescence on‐off sensing of volatile organic compounds and illustrate intrinsic charge‐transfer effects.

Sulfur- and Nitrogen-Containing Porous Donor–Acceptor Polymers as Real-Time Optical and Chemical Sensors

“…3.6 Å, 11 respectively (Figure S5). [16][17][18] Scanning electron microscopy (SEM) images of SNP-BDT1 and SNP-BDT2 networks confirm a 'cauliflower'-like morphology typical for nucleation-growth polymers, while the SP-BTT polymer grows in rod-like aggregates of 20 to 100 μm length (Figure S6-S8). Transmission electron microscopy (TEM) and selected-area electron-diffraction (SAED) for these three polymers confirm a similar degree of internal, microscopic structure as seen in PXRD data with visible, concentric rings indicative of polycrystalline materials (Figure S9-S11).…”

“…This has implications for the fluorescence life-times and the outstanding performance in photocatalytic hydrogen evolution from water of these D-A materials. [17][18] In this study, we make use of four key-properties of our conjugated, porous D-A polymersnamely, (1) their strong, covalent backbones, (2) their intrinsic Lewis acidity and basicity, (3) their permanently accessible pore channels to gaseous guest molecules, and (4) their optical bandgaps in the visible part of the spectrum -and we use them as optical and electronic sensors and switches that are triggered by volatile acid vapors and re-set by gaseous ammonia. While colorimetric chemical probes are known from molecular systems in solutions, [19][20] or work on the basis of chemical transformations, [21][22][23] the here-presented study shows one of the first instances of amorphous porous conjugated polymers used as fully-reversible, colorimetric chemical probes.…”

“…All polymers were prepared using the robust, Pd-catalyzed Stille cross-coupling to link the readily available, stannylated derivatives of thiophene-based molecules with halogenated triazine (TzCl 3 ) and tris-bromophenyltriazine (Tz(PhBr) 3 ) or sulfurcontaining benzotrithiophene (BTT-Br 3 ) monomers (see SI and Table S1). 18,25 Scheme 1. Synthetic pathway towards sulfur-and nitrogen-containing polymers (SNPs) and sulfur-only polymer, SP-BTT.…”

Modulating Benzothiadiazole‐Based Covalent Organic Frameworks via Halogenation for Enhanced Photocatalytic Water Splitting

“…The optical band gaps calculated from Tauc plots were about 2.25 eV, 2.36 eV and 2.34 eV for Py-HTP-BT-COF, Py-ClTP-BT-COF and Py-FTP-BT-COF (Figure 3 a), respectively, suggesting that all Py-XTP-BT-COFs are suitable for absorbing visible light for photocatalysis. [44] Meanwhile, the conduction band minimum (CBM) positions of Py-HTP-BT-COF, Py-ClTP-BT-COF and Py-FTP-BT-COF were estimated to be À2.76, À2.92 and À3.25 eV versus vacuum level, respectively, which should be able to reduce protons to H 2 . As shown in Figure 3 b, compared to the redox potentials (À4.02 eV versus the vacuum level) required for proton reduction at pH 7, [44] the electronic band structures of all Py-XTP-BT-COFs are well fitted for visible-light-driven hydrogen generation.…”

Sulfur- and Nitrogen-Containing Porous Donor-Acceptor Polymers as Real-Time Optical and Chemical Sensors

“…3.6 Å, 11 respectively ( Figure S5). [16][17][18] Scanning electron microscopy (SEM) images of SNP-BDT1 and SNP-BDT2 networks confirm a 'cauliflower'-like morphology typical for nucleation-growth polymers, while the SP-BTT polymer grows in rod-like aggregates of 20 to 100 μm length ( Figure S6-S8). Transmission electron microscopy (TEM) and selected-area electron-diffraction (SAED) for these three polymers confirm a similar degree of internal, microscopic structure as seen in PXRD data with visible, concentric rings indicative of polycrystalline materials ( Figure S9-S11).…”